The objective is to develop chemically defined diets that will consistently give an increase in the rate of growth when supplemented with growth promoting concentrations of antibacterial agents. Products and enzymes of intermediary metabolism will be studied in tissues and excreta to determine constituents that reliably predict an antimicrobial growth response. Major emphasis will be placed upon explaining the antibiotic growth response and how the diet of the animals can be improved to avoid the need for antibiotics for growth promotional purposes. Once information has been developed for rats and chicks, studies will be undertaken with growing swine. A major objective is to provide nutritional information which can lead to a reduction in the feed use of antibiotics by alternative methods and thereby to reduce the health hazard to man and animals which the FDA Task Force on the Use of Antibiotics in Animal Feeds reported after their intensive study. The studies are designed to generate information which would lead to more efficacious use of antimicrobial agents in animal production.